I haven't posted on here for a while, but I am running a workshop this weekend, getting some beginners started on the soldering addiction. I have rehashed some of my simple oscillator circuits and merged them into a single (strip)board that gives an LFO and VCO with PWM and headphone output - 6 knobs to twiddle and all running off a single 9V battery. Simple to construct, but capable of a good range of bleepy type sounds. All components easy and cheap to source. Basically designed to be an easily achievable first project that is simple enough for a beginner to build in a weekend, but sophisticated enough to make quite a satisfying range of cool sounds.

The new jpeg has a couple of things moved over slightly to make sure that the pots all have spare tracks either side of them. That makes it easier/safer if you are mounting the pots on the copper side (which is what I recommend). If you are mounting the pots on the copper side the legs of the pot need to be inwards towards the centre of the board, if you are mounting them through-hole you will need to have them oriented with their shafts inwards and legs nearer the edge. Hope that makes sense.

Also, I meant to say, that this circuit has now been built 5 times without problems so the layout is definitely good to go and is well suited to an educational setting where you can use it as the basis for teaching soldering, component identification, basic electronics including opamps, and some aspects of analog synthesis. About right for beginner adults or teenagers as long they have a reasonably good attention span. And at the end they have a little machine that can make some very cool sounds. A beginner (adult) who has never soldered before can build this (with a little bit of coaching) in about 6 hours of soldering. Plus a bit of extra one on one time at the end with someone to help them debug it and get it working. The only issues we had were the usual: placement off by one track, polarity wrong with diodes and electros, solder bridges between tracks, copper whisker bridges between tracks where they had been cut.

Played a gig last week making ambient noise with this as my sound source (together with two other guys playing mini modulars based on my circuits and a third guy playing a laptop as his sound source). This circuit above is definitely capable of a very cool and quite wide range of sounds. Especially with an effects pedal or two after it you can do a lot and those six knobs offer a lot of expression. Very happy with how it turned out

A recording was made at the gig, but right now that is two hours of audio that needs to get edited down by someone and I don't even have it on my computer to attack. It might be easier for me to specially record a little demo noodle to show a few of the sound possibilities. That way you could also get a chance to hear it dry and in isolation. I will see what I can do.

Not a very interesting video and the sound quality isn't great, but it gives you a pretty good idea of how we sounded. Of the four of us, I was playing this mini-synth circuit above (with delay and chorus), Adam was playing a mini-modular made up of various circuits of my design (2xVCO, LFO, VCLFO, S&H, VCA, VCF, ribbon controller), Dave was playing a VCO of my design plus running the mixer to blend us all together, Malcolm was using his laptop as a polyphonic oscillator. The sustained organ-like tones are Malcolm's laptop, but all the other stuff going on is from this circuit or other circuits of mine:

This is a lot of fun to play with. Mine will be coming out with me again tomorrow night to a gig. One thing I have been thinking about is that the aim was to create something monotron-like and one key feature lacking is an input socket to mangle other audio signals. I think the coolest place to inject some external audio would be the R7/R8/C5/D5 node. A resistor from that node (probably somewhere in the 33-100K range) to an input socket. I will try it sometime soon, but if anyone else gets the chance to try it first, please post here your comments on whether it is sonically interesting.

Question has come up ... "missing polarity markings on the capacitors c3,c4,c5. does it mean it doesnt matter?"

For these caps you need to buy unpolarised. Polarised caps like electrolytics and tantalums are marked and used for larger values. Pretty much all small value caps are unpolarised types. The 1uF cap is interesting because around that value you can get both polarised and unpolarised types, but in this case you need to make sure you get an unpolarised type and then it doesn't matter which way you solder it in.

The components I used just reflect what I had in my stash at the time. For things like R1, etc the value is not too critical, certainly anything within 30% would probably work fine. If you want to push the values beyond 20% either way then push them all as it is generally the ratios that matter. So if you want to use 1K for R1 then fine, but also use something a bit on the large side for R2, say 4-5K. Same for R3-R6, the values are not critical, but the ratios are what matters. Keep R3 and R4 the same as each other and roughly half of R5 and R6 which should be the same as each other. R7 and R8 can be varied quite a lot and it will affect the freq range, but not necessarily in a bad way None of the component values in this circuit are critical so have fun and make something unique by trying whatever you have to hand. The LM324 vs TL074 question is interesting, because it will almost certainly work and it may even work better, but it will probably sound slightly different at the extremes and it is at the extremes that this circuit is most interesting, ie when the LFO is almost stopped or when it is screaming in the upper audio - that is where it gets interesting - and that is where choice of op-amp may make a difference. But TL074 may be better, so go ahead and give it a go. As I said, nothing is critical in this circuit and everything is crying out for experimentation

Testing with a multi meter I see power in the circuit but it looks like it might be too low or something. Could it be due to c4 cap u state 220n I only had 100n caps and as such only used one. Could or should I use more.

Still new to electronics so pardon the simple questions and ignorance.

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